diff --git a/src/Instrumentation/marker_beacon.cxx b/src/Instrumentation/marker_beacon.cxx
index 816017a46..902ae20ad 100644
--- a/src/Instrumentation/marker_beacon.cxx
+++ b/src/Instrumentation/marker_beacon.cxx
@@ -297,6 +297,10 @@ void FGMarkerBeacon::search()
     _time_before_search_sec = 0.5;
 
     const SGGeod pos = globals->get_aircraft_position();
+    if (!pos.isValid()) {
+        // avoid error flood when core positions goes wrong
+        return;
+    }
 
     // get closest marker beacon - within a 1nm cutoff
     BeaconFilter filter;